Hardening of refractory/sodium silicate mixtures

ABSTRACT

SAND/SODIUM SILICATE AND ANALOGOUS MIXTURES ARE HARDENED BY A MIXTURE OF ETHYLENE GLYCOL MONOACETATE (EGMA) AND ETHYLENE GLYCOL DIACETATE (EGDA) IN WHICH THE WEIGHT RATIO OF EGMA TO EGDA IS 1:1 TO 1:9.

3,829,320 HARDENING OF REFRACTORY/SODIUM SILICATE MIXTURES Roger Philip Stanbridge, Cleveland, Ohio, assignor to Foseco international Limited, Birmingham, England 3,829,320 Patented Aug. 13, 1974 ice The surface active agent must be chosen with care, especially if it is to be made up and stored either with the sodium silicate or with the ester additive. If storage is not required, a mixture of sodium alkyl suiphonates 5 and secondary alkyl sulphates is satisfactory. If it is dec gg ggzgg" g sg ggg, gz i sg' r f i g 3 sired to mix the surface active agent with the sodium 32,39g 71 silicate, amphoteric or ampholytic surface active agents of Int. Cl. c041 35/16 general f u a US. Cl. 106-84 8 Claims 10 /CE: ABSTRACT OF THE DISCLOSURE I? (3H1 Sand/sodium silicate and analogous mixtures are hard- R-iZ-NCiH|OCHiCOONB erred by a mixture of ethylene glycol monoacetate o CHCOONB (EGMA) and ethylene glycol diacetate (EGDA) in which lh weight ratio Of EGMA 1O EGDA is 1:1 i0 129. wherein R is a capryfic or cthylhcxoic grou ar sati factory. This invention relates to the hardening of refractory T impioifhig efieei 0f e Small a diti s of su ac aqueou lkali t l ili mixtures active agent is greater at high concentrations of ester The invention will be described with particular refer- 12-16% based on the Weight of the Silicate) than ence to the hardening of sodium silicate/sand mixtures at i eoiieehifiihoiis 0f esler b s d o th as used, for example, for the production of foundry Weighi 0f the Silicate)- ould d cores, b i il b understood that the It is further found, that, in the case of foundry moulds invention is equally applicable to mixtures of sodium e cores, breakdown of h mould e after Casting silicate with other refractory materials such as magnesia, is h easiei- This y iii P hefiiie 9 c that, alumina or refractory silicates, or corresponding mixtures for a given final e gth, less sodium silicate need be using oth alk li t l ili a used, and the less, generally, the sodium silicate content,

Numerous additives have been suggested in the literaihe easier the rea down of the cores. ture for hardening sodium silicate/refractory mixes. The Preferred mixtures according the Pi f Many of these have been expensive, unstable or diflicult "PP ihiis consist of iefiaeieiy (Preferably eodliiiii to use because of too long or too short bench life of the sihcaie, a suifeiee aehye e G and G siiicate/refractory/additive mix. In addition, many addie P P the mixture of GM a d EGPA tives do not give hardened products of suflicientiy high used is Preferably iii ng of o 840% y Weight strength for many purposes. A further disadvantage of of ihe weighi 0f sodiiiiii e i Solids P some previous additives was that the refractory/silicate/ wide Variety Of eodiiiii} silicates y he iised- Sodium additive mix was very temperature sensitive. silicates 0f a 2 'e y he used, but 3 We have now found that particularly satisfactory re- P 2= 2 weight ratio range is A suits may be obtained by the use of a mixture of ethylene regards Solid-5 eeiiieiiis, eoiiieiiie 37-60% y Weight glycol mono-acetate (EGMA) and ethylene glycol diacemay he used, though P Solids eontents are 0- tate (EGDA) in a weight ratio of from 1:1 to 1:9 respecy itively. Thus, according to the present invention there is The lii'eseiit iiivehiioii i iii addition o t e mutid a hardenablc composition comprising a major tures noted above, additives for refractory (sodium siliproportion of a particulate refractory material and a P "fixtures which e a mixture of EGMA, F minor proportion bf a'hardening agent therefor, the hardin which the weight ratio f MA t0 EGD1 15 from ening agent comprising aqueous alkali metal silicate, eth- 1:1 9P "y eoiiiaiiiiiig Surface active ag yiene glycol monoacetate and ethylene glycol diacetate, e iiiveiiiidii fiii'ihei' iiiehides melhofi of i g a the weight ratio of ethylene glycol monoacetate to ethhofided i' P P which i p ee forming a ylene glycol diacetate being in the range 1:] to 1:9, mixture including refractory and sodium srlicate and as Such compositions have satisfactory bench lives, usudefined above, p g the miXlui'e, and allowing the ally in the ranges of 3-50 minutes at room temperature, 50 mixiiii'e haideii 9 give a hOiided fefilaeioiy P i i and lead to products of high strength. They are also rela- It is he if e h hardening eoiiipoeiheh tively insensitive to temperature. may also contain other ingredients known per se for We have found furthermore that if a surface active speeifie Purposes, g to aid hieakdowii, e031 agent is added to such a composition, then the results dust, P are even further improved. it is believed that this is due The following test iesiihs will serve to illustrate the to the surfactant aiding the dispersion of the mixture in nvention. The Surface active agent used in composition the sodium silicate and this leads to a more homogeneous 6 was a mixture of the two materials of which the strucmixture which enables less silicate to be used for a given tural formula is given above. All tests were carried out final strength. Conversely, for the same silicate usage, at a co stant temperature of 20 C. Compositions i and 2 higher final strengths are obtainable. The amount used are not mixtures according to the invention and are for of the surface active agent may vary, but will usually comparison purposes only. All parts and percentages are be less than 1.00% of the weight of sodium silicate in by weight. the mixture. Generally from ODS-0.7% by weight, based Four compositions not containing a surface a ti on the weight of sodium silicate, is satisfactory. agent were made up and tested as follows:

Composition 1 2 3 4 Band, parts 1 1m mg Sodium silicate, parts 3.5. 3.5. 8.5- 3,5, n r Mixture O EGDA, Mix Mmm B,

0.42 part. 0.42 part. 0.42 part. 0.42 part.

i Silica sand A.F.A. rain fineness number 60. I Weight ratio S102! 810 2.5:1, solids content 43.6%.

Nora-Mixture A was 17 parts EGMA, 83

parts EGDA; Mixture B was 28 parts EGMA 72 parts EGDA; Mixture C was a commercial EGMA: 40 parts EGDA and 5 parts glycol. grade of EGMA containing 55 parts 3 (1) The working time or bench life of sand compositions This was tested by preparing standard A.F.A. compacts at various intervals after mix preparation, allowing these to harden for 24 hours in a sealed container (to eliminate variations in strength due to the evaporation of moisture during setting), and determining the compression strength using a l-lounsfield tensometer. A reduction in attainable strength below 200 lb./in.= defines the maximum working time of bench life of the sand composition.

Composition 1: Compression strength Core preparation time after 24 hours after mixing (mins.): (lb./in.

Core preparation time after mixing (mins.):

V; 255 1 190 2 168 3 112 4 72 5 40 Estimated Bench Life less than 1 minute.

Composition 2:

Core preparation time after mixing (mins.):

120 400 130 193 Estimated Bench Life 125 minutes.

Composition 3:

Core preparation time after mixing (mins.):

450 290 4 192 Estimated Bench Life 37 minutes.

Composition 4:

Core preparation time after mixing (mins.):

Established Bench Life 5 minutes.

(2) Strength development characteristics These determined by preparing test cores immediately after mix preparation, allowing these to harden in an enclosed container, and determining compression strengths at various intervals after core preparation.

Composition 1:

Hardening time (hrs.):

4 Composition 2: Composition strength Hardening time (hrs.): (lb/in?) /1 0 1 0 2 0 3 166 4 266 5 315 24 534 Composition 3:

Hardening time (hrs.):

Composition 4:

Hardening time (hrs.):

Compositions tested 6 6 Sand, parts 100 100 Sodium silicate, parts 2. 6 2. 5 Hardener, mixture A, part. 0. 40 0. 40 Surface active agent, part Nil 00126 Both of these compositions had "bench lives" of approximately 20 minutes.

Strength development characteristics Composition 5 Compression strength It can be seen that compared with compositions merely comprising sodium silicate, refractory and EGDA, or an EGMA/EGDA, mixture with more EGMA than EGDA, the compositions of the invention give improved results with respect to final compressive strength and bench life.

The following test indicates the decrease in temperature sensitivity of the composition of this invention.

Mixture were made up as composition 3 above and as composition 3 but with a commercial hardener substituted for Mixture A. The commercial hardener had a composition by weight of 75% triacetin and 25% diacetin. The mixing was carried out at various temperatures and bench life determined as noted above.

Results were as follows:

Bench life (mins.) M

Wit Composicommercial tion3 hardener Mixllnog temp. 0.):

Compression strength Percent after 24 hours, p.s.i. increase in compression Without With strength due sur ce surface to surface active agent active agent active agent Amount oi mlftslilli'ie .teas a percen e ca It is clear that the usefulness of adding surface active agent is more pronounced at higher ester usages.

I claim as my invention:

1. A hardenable composition consisting essentially of a major proportion of a particulate refractory material and a minor proportion of a hardening agent therefor present in an amount sufficient to cause hardening, the hardening agent consisting essentially of aqueous alkali placed in sealed containers at room metal silicate, ethylene glycol monoacetate and ethylene glycol diacetate, the weight ratio of ethylene glycol monoacetate to ethylene glycol diacetate being in the range 1:1 to 1:9.

2. A composition according to claiml wherein the particulate refractory material is sand.

3. A composition according to claim 1 wherein the alkali metal silicate is sodium silicate of SiO :Na,O ratio 2.0 to 3.3.

4. A composition according to claim 3 wherein the combined amount of ethylene glycol monoacetate and ethylene glycol diacetate is 8-20% by weight of the weight of sodium silicate solids.

5. A composition according to claim 3 which includes a minor proportion of a surface active agent.

6. A composition according to claim 5 wherein the amount of surface active agent is 0.05% to 7% by weight of the sodium silicate solids.

7. A composition according to claim 1 and including a minor proportion of a material selected from the class consisting of sugars, coal dusts and pitches.

8. A method of forming a bonded particulate material which comprises mixing a major proportion of particulate material, a minor proportion of an aqueous alkali metal silicate and a minor proportion of a hardener consisting essentially of a mixture of ethylene glycol monoacetate and ethylene glycol diacetate in which the weight ratio of ethylene glycol monoacetate to ethylene glycol diacetate is 1:1 to 1:9, forming the mixture to the desired shape'and allowing the mixture to set to form a bonded product.

References Cited UNITED STATES PATENTS 3,138,471 6/1964 Wygant 106-84 3,149,985 9/1964 Gandon 106-74 3,493,406 2/1970 Fillet et a1. 106-84 JAMES E. POER, Primary Examiner US. Cl. X.R. 106-3835 

